I want to have shared folders between my computer on Arch Linux and a virtual machine with ReactOS, but I don't know where the folder appears in ReactOS.
Where does it appear?
Solution
Do it as you would do on Windows:
Install VirtualBox Guest Additions in your ReactOS VM
Define your shares in your virtual machine configuration (through VirtualBox interface)
Reboot your ReactOS VM
If you checked automount in the VirtualBox GUI, they'll be already available, mapped as a drive letter in the explorer. If you didn't, then either go to 'Network Places' to find them, or directly type the UNC path in the explorer address bar, or use the 'net use' command line tool